Optical Energy Transfer and Conversion System for Planetary Rover having Axially Configured Fiber Spooler Mounted Thereon

ABSTRACT

An optical energy transfer and conversion system comprising a fiber spooler and an electrical power extraction subsystem connected to the spooler with an optical waveguide. Optical energy is generated at and transferred from a base station through fiber wrapped around the spooler, and ultimately to the power extraction system at a remote mobility platform for conversion to another form of energy. The fiber spooler may reside on the remote mobility platform which may be a vehicle, or apparatus that is either self-propelled or is carried by a secondary mobility platform either on land, under the sea, in the air or in space.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a divisional application claiming priority to and the benefit ofU.S. application Ser. No. 14/810,121, filed Jul. 27, 2015, and entitled“Optical Energy Transfer and Conversion,” which is a continuationapplication claiming priority to and the benefit of U.S. applicationSer. No. 13/303,449, filed Nov. 23, 2011, which claims priority to andthe benefit of U.S. provisional application Ser. No. 61/416,676, filedNov. 23, 2010, all of which are hereby incorporated by reference herein.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with Government support under Grant No.NNX10AE29G awarded by NASA. The Government has certain rights in theinvention.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to power systems. More specifically, thepresent invention is a system for the transfer of optical energy to aremote location and subsequent conversion of the transferred opticalenergy to another form of energy such as heat, electricity, ormechanical work.

2. Description of the Related Art

It has been known in the telecommunications industry for several decadesthat light, or optical energy, can be sent down a relatively smalldiameter (e.g., twenty-five micron) glass optical fiber, modulated, andused to send large amounts of low-noise data or voice channels in amanner superior to traditional metal conductors. The range (i.e.,distance) over which an un-boosted signal can be sent down such a glassfiber is controlled by a number of physical phenomena along with thegeometry of the fiber and the materials used in its construction.

As light travels down the fiber, a portion of the injected energy islost due to several mechanisms including Rayleigh scattering, OHabsorption, imperfection loss, and infrared absorption. First, Rayleighscattering is a function of the wavelength of the injected laser lightand of the fiber material (frequently silica glass). Aside fromselecting a low impedance fiber, the only way to reduce Rayleighscattering is to select the wavelength of light that produces the leastpower loss per unit length of fiber. Second, OH absorption loss can becontrolled or reduced by constructing fibers with ultra low OH contentand avoiding wavelengths that coincide with wavelength-specific OH losspeaks. Third, imperfection loss can only be reduced by use of a fiberwith minimal or no manufacturing imperfections. Often this is an issueof quality control of raw materials and manufacturing processes thatdraw the fiber slowly so as to not introduce imperfections. Finally,infrared absorption loss is a function of wavelength and material. Asidefrom material selection and improvement infrared loss can only beminimized by choosing an optical frequency that minimizes the losses.

In addition to the optical transmission loss mechanisms just described,there are other potential power loss mechanisms including: thermaldamage to fiber at very high temperatures (whether externally orinternally produced); non-linear effects such as SRS (stimulated Ramanscattering), and also “self-focusing.” Self-focusing has been predictedto potentially limit actual power delivery in a fiber to four or fivemegawatts regardless of fiber diameter, based on current theoreticalassumptions and predictions. However, as with many previous theoreticalpredictions relating to estimates of power and power density limitationsfor lasers, these estimates may also prove overly conservative in time.

FIG. 1A shows a plot of the theoretical composite attenuation limits foroptical power transmission as a function of wavelength per kilometer ofpure silica fiber. Other materials and fiber constructions (e.g.,hollow, mirror-coated fiber) will have different attenuationcharacteristics. However, currently, pure silica fiber is the mostreadily available material to work with and obtain in long lengths (onthe order of tens of kilometers). The composite attenuation is at aminimum at approximately 1540 to 1550 nanometers (nm) wavelength. Thisis due mainly because Rayleigh scattering decreases with increasingwavelength, but after a certain wavelength infrared losses begin todominate, thus producing a distinct minimum attenuation, which ischaracteristic for pure silica. Other materials—and in particular, otherdoped optical materials—may exhibit different frequency response.

As a consequence of FIG. 1A, and for a wavelength of injected lightbetween 1540 to 1550 nanometers with an initial injection power level ofone megawatt, FIG. 1B shows the theoretical limiting optical powertransmission as a function of the length of fiber, indicating that asfar as one-hundred kilometers from the laser source, that an outputpower of approximately fifty kilowatts (kW) is achievable. This level ofoutput power is significant, and sufficient to enable a host of novelapplications.

FIG. 1B is a theoretical construct. Prior to the work of the inventors,fiber optics have been limited to low power data communicationsapplications and limited “power over fiber” demonstrations at very lowpower levels (on the order of milliwatts) over standardtelecommunications fiber. At the other end of the spectrum, industrialcutting lasers, many powered by fiber lasers, have used a very short(typically less than ten meters in length) “process” fiber for transferof the laser energy to a local cutting head adjacent the laser and inthe same building.

The concept of very high power transfer over very long distances had notbeen investigated. The inventors, in the fall of 2007, beganinvestigating the concept of using optical fiber to send tens ofkilowatts of optical energy to an ice penetrating robotic system as ameans of enabling a test of a planetary ice-cap penetrating sciencevehicle for the investigation of the polar ice caps of Mars as well asthe planetary ice cap of the Jovian moon Europa. The concept was drivenby a need to achieve thermal power levels at the robotic system thatwere similar to those that would be developed by a systems nuclearauxiliary power (SNAP) thermal reactor (on the order of several tens ofkilowatts) without the use of nuclear power, as the likely testinggrounds for the system would be Antarctica, where present treatiesprohibit the use of nuclear power.

In early July 2010, the inventors conducted a high power, long rangelaser power transfer test that utilized a twenty-kilowatt infrared (1070nanometer) fiber laser wherein power levels from zero to ten kilowattswere incrementally injected into a 1050-meter long coil of multi-mode,step index, pure silica core, fluoride doped cladded with polyimidecoating (400 μm core, 440 μm cladding, 480 μm coating diameters). Thefiber numerical aperture (NA) was 0.22.

FIG. 2 shows the results of that test, which compare favorably with thetheoretical attenuation limits shown in FIG. 1A. The fiber was coiledinto a one-meter diameter spool which was water cooled in a static flowbath, the temperature of which was monitored. The power was ramped upfrom one hundred watts to ten kilowatts over an approximately one-hourperiod. After five minutes at ten kilowatts, the peak temperature of thefiber was fifteen degrees Celsius above ambient as monitored using aforward looking infrared (FLIR) camera. This test pushed new boundariesin terms of the injected power levels sent through an optical fiber butalso contradicted traditional thinking in the high power process laserindustry that the power would have been completely dissipated by thelarge number (334) of bends to the fiber in the process of fabricatingthe coil.

With this as a background, we now discuss some important recent factorsthat enable practical implementation of the systems that willsubsequently be described below. FIG. 3A shows a plot of raw industriallaser continuous output in kilowatts versus year for a single mode fiberlaser. These were laboratory curiosities in the early 1990s. In 2009,however, an output level of ten kilowatts was achieved for a 1070 nmindustrial fiber laser. It is important to note that with fiber lasersit is possible to combine several single mode lasers by injecting theirindividual beams into a multimode fiber. To date, multimode fiber lasershave achieved power levels of fifty to sixty kilowatts through onemultimode fiber, operating over a short distance of process fiber (lessthan ten meters) between the laser and its output optics.

An equally important measure of progress is that of power density,expressed in megawatts per square centimeter (MW/cm²). FIG. 3B plotspower density in MW/cm² since 1994. A more practical means ofunderstanding what this graph means is presented in FIG. 3C, in whichthe LOG of power density is plotted. This plot indicates that, at thecurrent pace of development, which has been sustained since 1994, thepower density will increase by an order of magnitude every six years.

Finally, FIG. 3D shows the theoretical power that can be transferredthrough a fiber optic carrier as a function of fiber core diameter (inmicrons) using optical power densities achieved in 2009. A three-hundredfifty micron core fiber is capable, today, of carrying a megawatt ofoptical power. FIG. 1B, as previously discussed, shows the output powerthat could be expected as a function of distance from the laser for acontiguous fiber.

The data presented in the figures referenced supra presage thepossibility of sending enormous amounts of optical power over very longdistances using very small diameter, lightweight fibers and convertingthat optical power to a more usable form of energy. Importantly, becausethe fiber is carrying the power, it will not be attenuated by theenvironment surrounding the fiber nor by a situation wherein theconsumer of the power is not in visible line-of-sight of the sourcelaser. This has profound implications on the development of many systemsheretofore not considered possible.

FIG. 4 shows the very basic premise of the transfer of coherent highpower laser radiation between a laser source 22 and a remote system 36in which a base power source 20 (e.g., a nuclear power plant, a fossilfueled power plant, a large diesel generator, a very large array ofsolar cells, etc.) is used to provide electrical power to the high powerfiber laser 22 via electrical conductors 24. Currently, the best fiberlasers are on the order of thirty-five percent power conversionefficiency (i.e., for every ten watts of raw electrical power,three-and-a-half watts of coherent laser radiation can be produced).Because of this, the laser 22 dissipates a substantial thermal heatload. To counteract this, a cooling system 26 and heat transfer system28 is used to maintain thermal control at the laser. All of thisinfrastructure takes up volume, has significant mass, and consumes largeamounts of power. It is therefore best located in some fixed groundfacility or a large mobile facility (e.g., a ship). From the laser 22, ahigh energy process fiber 30 leads to a high power optical coupler 32,to which any number of devices can be connected. Traditionally, the onlyitems to be connected to this category of multi-kilowatt laser arefocusing optics for use in materials handling—e.g., cutting metal platesor fabric. Because of this, the length of the process fiber 30, 34 aregenerally quite short—on the order of five to ten meters.

The present invention relates to a system and apparatus that enables thetransmission and effective end-use of very large amounts of opticalpower (e.g., kilowatts to tens of megawatts) over relatively longdistances (e.g., from a kilometer to as much as one hundred kilometersor more) to fixed, movable, or mobile platforms operating on the ground,undersea, under ice, in the air, in space, and on other planets. Theinvention is usable in non-line-of-sight conditions, which allows it todirectly bypass severe problems that have plagued efforts to utilizelaser power beaming over large distances through the atmosphere,underwater, and over terrain where the receiver is not within view ofthe optical power source. The present invention permits first kilowattand then ultimately multi-megawatt optical power injection andutilization over the length of a long deployed fiber.

BRIEF SUMMARY OF THE INVENTION

The invention is an optical power transfer system comprising a fiberspooler and an electrical power extraction subsystem connected to thespooler with an optical waveguide. Optical energy is generated at andtransferred from a base station through fiber wrapped around thespooler, and ultimately to the power extraction system at a remotemobility platform for conversion to another form of energy. Analternative embodiment of the invention further comprises a fiber opticrotary joint mechanically connected to the fiber spooler, with the fiberoptic rotary joint positioned optically between the spooler and thepower extraction system.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1A shows a plot of the theoretical composite attenuation limits foroptical power transmission as a function of wavelength per kilometer ofpure silica fiber.

FIG. 1B shows a plot of the theoretical limiting optical powertransmission as a function of the length of fiber.

FIG. 2 is a plot of a high power, long range laser power transfer test.

FIG. 3A shows a plot of raw industrial laser continuous output versusyear for a single mode fiber laser.

FIG. 3B plots power density in MW/cm² since 1994.

FIG. 3C plots the log of the power density of FIG. 3B for a single modefiber laser.

FIG. 3D shows a plot of the present optical power transmission as afunction of fiber core diameter.

FIG. 4 shows the basic premise of high power laser radiation transferbetween a plant fiber laser system and a remote system.

FIG. 5A shows a first variation on the optical, long-range powertransfer invention of the present invention.

FIG. 5B shows a second variation of the invention incorporating an axialprecision-wound spooler.

FIG. 5C is a detailed example of an embodiment involving a singleexterior mandrel, precision-wound high energy optical fiber spooler.

FIG. 5D shows a cut-away detail of the exterior wrapped mandrel of FIG.5C.

FIG. 5E is a top isometric view of the same external fiber spooler andprotective shell system described with reference to FIG. 5C.

FIG. 5F is a variation on the axial high power fiber spooler 50 in whichthe mandrel 60 defines winding grooves 86 on the interior surface.

FIG. 5G shows yet another variation on the high power axial fiberspooler 50.

FIG. 5H shows a cross sectional detail of an embodiment of a drum-typehigh energy fiber spooler such as shown in FIG. 5A.

FIG. 6 depicts an alternative embodiment of the system in which thefiber spooler is carried onboard a remote system or mobile system.

FIG. 7 is a system diagram of the electrical power extraction subsystemof the system.

FIG. 8 is a isometric view of mobility system power head 160implementing the invention.

FIG. 9 is a sectional view of an embodiment of a fiber optic rotaryjoint (FORJ) that can be used with the present invention.

FIG. 10 is a sectional view of another embodiment of a FORJ that can beused with the present invention.

FIG. 11 shows an exemplary laser connector suitable for use in thepresent invention.

FIG. 12 shows an embodiment of the system in use with Beta-type Stirlingengine.

FIG. 13 shows an embodiment of the system in use with an autonomousunderwater vehicle.

FIG. 14 depicts a mission configuration for the autonomous vehicle shownin FIG. 13.

FIG. 15 shows a system schematic for an autonomous cryobot.

FIG. 16 shows an embodiment in use with an exploration and sciencerover.

FIG. 17 shows another embodiment in use with an underwater vehicle.

FIG. 18 shows an embodiment in use with a launch vehicle.

FIG. 19 shows an embodiment having a central spooler in use withmultiple thrusters.

FIG. 20 shows an alternative arrangement of the system of FIG. 19.

FIG. 21 shows an embodiment using a rotary beam switch with multiplespoolers.

FIGS. 22-23 show an embodiment in use with an unmanned aerial system.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 4, in the present invention, the length of the outputfiber 34 is desirably a long distance—from a few kilometers to upwardsof one hundred kilometers or more—and used for the purpose of providing,specifically, optical energy to a remote actuation system 36 thatconsumes the power in a variety of ways for the purposes of mobility,propulsion, raw thermal power utilization, electrical power conversion,mechanical power extraction or for the purpose of using the laser energyitself in a focused beam.

Referring now to FIG. 4 and FIG. 5A, one could conceive of setting upsuch a system whereby a truck is used to lay fiber 34 from theplant-based (fixed) fiber laser system 16 to a fixed actuation system ordevice 36 that uses the energy at some significant distance from thelaser source 22. In general, this will have very limited utility becauseit would be, under most conditions, equally possible to use a localpower source at the location of the remote system 36 and not pay theprice for the power lost along the fiber 34. In other words, traditionalelectric power infrastructure will be more cost competitive thandeploying a fixed infrastructure that depends upon power sent to it viaan optical waveguide or fiber. This is not the case, however, when wewish to consider mobile systems that perform a variety of tasks andwhere it is entirely disadvantageous, if not impossible, for the mobilesystem to carry all of the extensive infrastructure needed to generateits own power.

FIG. 5A shows a first embodiment on the present invention in which thebase station 16 comprises a servo-controlled large-diameter drum spooler38 fabricated from a high thermal conductivity material (e.g., berylliumoxide, copper, or aluminum) to facilitate cooling. A large length(kilometers) of fiber 40 is rolled onto this spooler 38 prior to amission in which the remote system 18 (e.g., a vehicle) is sent forth todo work. As the vehicle leaves the base—for example, a large sea goingship, where the vehicle is an underwater vehicle such as an autonomousunderwater vehicle (AUV) or remotely operated vehicle (ROV)—the drumspooler 38 will rotate and feed fiber 40 out to the vehicle. Thisapproach will work well in the restricted situation where there are noobstacles in the path of the vehicle that might serve to trap the fiber40 and prevent return of the vehicle. For example, it would work wellfor sea-going operations and could potentially be made to work, usingbare fiber, for aerial operations where the base station 16 was carriedby a large lighter-than-air airship and the remote vehicle 18 was anunmanned aerial vehicle (UAV) connected to the airship via a bareoptical fiber for weight reduction.

The drum spooler 38 has several important characteristics, including anactively-cooled high power laser coupler 42 that will permit easymaintenance of the drum spooler 38. Because of the high power levelsinvolved, the spooler 38 must have an active cooling system 44. Thereason for this is that not only will power be dissipated along thelength of the fiber 40 by the normal Rayleigh scattering and infraredradiation, but it is also compounded by additional losses associatedwith the bend radius of the fiber 40. Bending losses are a function ofthe fiber construction (e.g., core, cladding, coating styles, andrefractive indexes), the fiber diameter, the bending diameter, and thelaser power conditions entering the bending section. Bending losses willbe controlled by selecting a combination of fiber type, size, andconstruction along with an appropriate spooler diameter for the specificapplication. The cooling system 44 can consist of any traditional meansfor transferring excess heat away from the spooler 38, including, butnot limited to, heat exchangers, convective, conductive, and radiativecooling mechanisms (see FIGS. 5C-5H).

Importantly, the drum spooler 38 is mechanically connected to ahigh-energy fiber optic rotary joint 46, as will be described in moredetail with reference to FIGS. 9-10, in which a fixed fiber thattransfers optical power at high levels through coupler 42 is channeledto the core of the spooler 38 which rotates freely relative to the fixedcoupler 42. This is required to avoid unacceptable twisting that wouldultimately lead to failure of the fiber 40. The design of a viableultra-high-power fiber optic rotary joint is a complicated undertaking.

The drum spooler 38 is desirably of large diameter to limit power lossassociated with bending of the fiber to form the cylindrical (or othersimilar object of revolution) spool. Power loss associated with bendingcan be minimized by using a large bend radius, using smaller diameterfiber, and fiber with a high numerical aperture (NA). Preferably, thediameter of the spooler 38 needs to be large enough that the powerlosses due to the bending of the fiber do not heat the fiber excessivelyfor the given cooling conditions and they are an acceptable percentageof the total power (i.e., within acceptable losses).

The diameter and all other bending loss parameters are designed to keepthe bending losses at an acceptable level. The level of loss will dependon cooling requirements of the particular application: some applicationswith good cooling and no need for high efficiency can have large lossesand thus possibly smaller diameters, while systems with poor cooling andneeds of very high efficiency will require lower losses and thustypically larger diameters. This is extremely complex and based on manyvariables. Bending losses are a function of the fiber construction(e.g., core, cladding, coating styles, and refractive indexes), thefiber diameter, the bending diameter, and the laser beam conditionsentering the bending section (beam NA multimode/single mode/specificmode content for multimode, etc.)

The selection of the fiber 40 is based on several criteria: it shouldhave low losses associated with Rayleigh scattering, Raman scattering,and infrared radiation; it should have an ultra-low OH content;preferably have a high NA; have high tolerance to external heat load; beable to operate in fluids without degradation to the fiber's ability totransmit power; be free of imperfections in the manufacturing process;and have a durable cladding that permits reasonable handling toughnessboth during the winding and out-spooling events. A preferable fiber hasa pure fused silica core, with doped silica cladding to give a change inthe index of refraction, which allows the light to be guided with a NAbetween 0.22 and 0.37.

Bare or armored fiber 40 exits the drum spooler 38 and thencecommunicates with the remote system 18, which could be any device,vehicle, or apparatus that is either self-propelled or is carried by asecondary mobility platform either on land, under the sea, in the air,in space, or on Earth or another planet. Desirably, the remote system 18is equipped with a high power fiber optic coupler 32′ so that it can bedesirably disconnected from the power plant 16 for maintenance andtransport between missions. The fiber internal to the mobility system 18then terminates in a fixed actuation system or device 36 that makes useof the optical power by converting it to another form of energy.

FIG. 5B shows a variation of a power plant 16 incorporating aprecision-wound axial spooler assembly 50. Instead of a drum spooler (asshown in FIG. 5A), the axial spooler 52 is one in which the fiber 40 ispre-wound in such a fashion that it may be pulled out parallel to theaxis of the winding without causing the fiber 40 to twist or hockle.Typically, this requires precision winding equipment that inserts apre-twist of a certain amount per wrap such that the fiber 40 can pullfree in the direction of the axis without twisting.

The nature of the winding must be special for a high power applicationin which large amounts of energy are transmitted through the fiber 40.These details are discussed with reference to FIGS. 5C-5H. At a minimum,however, a high energy axial fiber spooler assembly 50 will require anactive cooling system 54 that chills the fiber 40. An auxiliary passivethermal power dissipation system 56 may be desirable to further transferunwanted heat to the environment (whether underwater, on the ground, inair, or in space).

A plant-based fiber spooler can be quite large in diameter and thereforelimit bending losses. In general, axial spoolers are consideredone-time-use devices because there is no reliable nor economical fieldmethod for re-spooling and making re-use of the fiber in the fashionthat would be possible for a ship-based drum spooler working withjacketed (armored) fiber. Similar to the drum spooler 38 described withreference to FIG. 5A, the axial spooler 50 contemplates high poweroptical couplers 32 on opposing sides so that it may be field-connectedto the laser 22 and to the remote system 18.

FIG. 5C shows a detailed example of one embodiment of a single exteriormandrel 60 referenced with respect to FIG. 5B. A hollow or solid windingmandrel 60, which is preferably made of a high thermal conductivitymaterial (e.g., beryllia, copper, aluminum), has bare optical fiber 62wound upon its radially exterior diameter in such a fashion that directaxial pull out parallel to the mandrel axis 64 is possible withoutintroducing twists to the fiber 62. This can be achieved by pre-twistingthe fiber 62 during the precision winding process. The bare fiber 62exits the rear of the spooler 50 and trails in the direction of thelaser power source 22. The vehicle moves in an opposite direction 66along the same axis. The fiber 62 is preferentially attached to mandrel60 by a high thermal conductivity adhesive (e.g., materials consistingof a base synthetic polymer system containing thermally conductivefillers) such that the adhesive transmits heat directly to the mandrel60 in an efficient manner and also lightly binds the fiber 62 to themandrel 60 so that it does not unspool without a constant tension beingapplied by the exiting fiber 62, said allowable tension level beingspecific to a particular fiber design and diameter, but with the generalcharacteristics of both binding the fiber 62 to the mandrel 60 so thatindividual fibers do not slide freely relative to one another and yetnot so high as to impede the free spool out of the fiber 62 to a degreewherein it may stress the fiber 62 to a point at which it either breaksunder tension or adversely affects the transmission of power (e.g., bycross-sectional thinning under tension). Examples of appropriateadhesives are ResinLab EP 1121-4, Dow Corning SE4450, and the like.

The mandrel 60 will require active cooling for high power applications.To achieve this, internal flow channels 68 are disposedcircumferentially through mandrel 60 and are fed by an inlet 70 andexhausted by an outlet 72. The coolant, which may be either activelypumped or passively fed through the channels 68, can be drawn: from theambient environment in the event that that fluid has a high heatconduction capacity; from a reservoir of high heat conduction capacitycoolant (e.g., water, liquid metals etc.) that is actively chilled (andthermal power dissipated non-local to the spooler 50); or from areservoir of cold material (e.g., cryogenic liquids). In addition,coolant can be caused to flow through the center of the mandrel 60 toprovide further heat removal from the spooler 50.

The spooler 50 has an exterior protective housing 74 that also functionsas a thermal radiator. The housing 74 may preferentially have athermally absorbing coating applied to the radially interior surface 76such that any heat radiated from the spooled fiber 62 is preferentiallyabsorbed by the housing 74 and thermally-conductive coating. The housing74 further may desirably have internal coolant flow channels 78 that mayreceive fluid flow from any of the aforementioned coolant sources. Thehousing 74 may furthermore be advantageously equipped with exteriorradiation panels 80 extending along the length of the housing 74. Thethermally absorbing coating has good absorbing ability in the infraredspectrum.

Yet another means for removing heat from spooler fiber 62 is that ofdirected flow of a coolant via inlet ducts 82 that direct the coolingfluid to pass lengthwise down the axial assembly via a fiber feedchannel 84 formed between the mandrel 60 and the housing 74, and fromwhich the fiber 62 ultimately exits the spooler 50.

One purpose of all of these features is to maintain the fiber 62 withina working temperature range that will not affect the material orfunction of the fiber 62 for the transmission of high power opticalenergy. Silica, and most materials suitable for the purpose of opticalpower transmission down a small diameter fiber, has a very low thermalconductivity so it acts to impede cooling of adjacent fibers throughcontact. For this reason, and as shown in FIG. 5C, the most efficientfiber spooler for high power optical energy transmission is one thatcontains only a single layer, or only a few layers, of bare fiber 62.Depending on the power levels involved, additional layers may be addedand the flow of coolant through channels 68 and other coolantcommunication paths adjusted accordingly to maintain fiber temperaturewithin the specifications for the selected fiber.

Not shown on this drawing, but of significance to the operation of thissystem, is a network of surface-mounted temperature sensors that can beused to detect an impending hot spot that may cause the fiber 62 to faillocally or regionally. In this case, these temperature sensors can betied to the active thermal control system as well as to the laser for apre-emptive beam shut down in the event of an uncontrollable buildup ofheat in any particular section of the assembly.

For reference, a single wrapped axial spooler mandrel that is two-tenthsof a meter in diameter by one-half meter in length can carry 1.3kilometers of 250-micron fiber in a single layer; 2.6 kilometers in adouble layer; 3.9 kilometers in a three-layer wrap, etc. There are meansfor building much longer, high power axial spoolers, as will besubsequently described below.

FIG. 5D shows a cut-away detail of the exterior wrapped mandrel 60 fromFIG. 5C. Desirably, for improved heat conduction, the exterior surfaceof the cylindrical mandrel 60 will contain a smooth, form-fitting groove86 designed to precisely mate with the chosen bare power delivery fiber.The groove 86 would be preferentially manufactured using a precisionmachining system or other method of creating a spiral, continuous groove86 the local radius of which either precisely matches or is slightlylarger than that for the chosen power fiber. The degree of machiningdepth will represent the minimum needed for secure fiber location. Forvery high power applications, the spacing (pitch) between individualcoils of the groove 86 should be such that the adjacent fibers do nottouch each other. Further, the edges 88 between the respective grooves86, as well as the groove surfaces, preferably are polished and have asmooth transition radius such that there are no sharp edges anywhere onthe face where the fiber is to be wound. Similarly, the interiortrailing edge 90 and the exterior trailing edge 92 have a smooth radiusand are polished to prevent fiber damage on spool-out. An alternative tothe spooler design shown in FIG. 5D would involve the use of a smoothpolished cylindrical external winding surface (replacing the polishedgrooves 86 and 88 in FIG. 5D), or one that is slightly tapered (with orwithout alignment grooves 86) toward the direction of fiber spool out sothat the diameter of the tapered, truncated conical annulus is less atthe point of fiber departure (64 in FIG. 5C) than it is at the opposingend (in the direction of vehicle motion, 66 in FIG. 5C). In both cases,the fiber is adhered to the smooth, polished surface by means of athermally conducting adhesive means and, desirably, the fiber spacing issuch that adjacent fibers do not touch. Multiple fiber layers, heldtogether by a thermally conducting adhesive means, are possible onmandrels as shown in FIG. 5D (and as described in this paragraph),however the ability to effectively cool the multiple wraps will bediminished relative to a single-wrap mandrel and careful thermal designwill be required to determine the maximum number of over-wraps for agiven power transmission level, mandrel wrapping radius, and diameter ofthe transmission fiber, among other things.

FIG. 5E shows a top isometric cutaway view of the same external fiberspooler 50 and protective housing 74 described with reference to FIG.5C. Importantly, the direct axial flow cooling fluid inlet ducts 82 arenotional representations only. For travel through a fluid medium (e.g.,water or air) there can be present computer-controlled, servo panelsthat open to permit either water or air to be drawn into the vehicle asit moves forward and to channel that fluid down into the fiber feedchannel 84 for the purposes of cooling the radially exterior surfaceface of the fiber 62. Because the fiber 62 must freely trail out fromthe channel 84, any cooling fluid that passes into inlet ducts 82 willexit the fiber feed channel 84 after one pass and not be able to bere-used. Contrarily, any fluid or coolant pumped through circumferentialchannels 68, 78 can be re-cycled and sent to an alternate location inthe vehicle either for the purpose of refrigeration of the coolant orpotentially for pre-heating of a working fluid or propellant.

FIG. 5F shows a variation on the axial high power fiber spooler 50 inwhich the mandrel 60 defines winding grooves 86 on the interior surface.All other aspects of this design remain the same as for those shown inFIGS. 5C-5E, including the presence of circumferential cooling channels68. Importantly, such a winding pattern depends on the use of thethermally-conducting adhesive to lightly attach each fiber to the groove86 as the fiber 92 is precision-placed. The groove 86 forms a continuousspiral (helix) and the fiber 62 pays out linearly in a directionparallel to the center axis of the cylindrical mandrel 60. As discussedsupra, for the highest power applications, it is desirable to have asingle wrap of fiber 62. For lower power applications it will bepossible to have several layers of wrapping.

An alternative to the spooler design shown in FIG. 5F would involve theuse of a smooth polished cylindrical internal winding surface (replacingthe polished grooves 86 in FIG. 5F), or one that is slightly tapered(with or without alignment grooves 86) toward the direction of fiberspool out so that the diameter of the tapered, truncated conical annulusis greater at the point of fiber departure (64 in FIG. 5C) than it is atthe opposing end (in the direction of vehicle motion, 66 in FIG. 5C). Inboth cases, the fiber is adhered to the smooth, polished surface bymeans of a thermally conducting adhesive means and, desirably, the fiberspacing is such that adjacent fibers do not touch. Multiple fiberlayers, held together by a thermally conducting adhesive means, arepossible on mandrels as shown in FIG. 5F (and as described in thisparagraph), however the ability to effectively cool the multiple wrapswill be diminished relative to a single-wrap mandrel and careful thermaldesign will be required to determine the maximum number of over-wrapsfor a given power transmission level, mandrel wrapping radius, anddiameter of the transmission fiber, among other things.

FIG. 5G shows yet another variation on the high power axial fiberspooler 50. An exterior mandrel 60 of this spooler 50 is the same asshown in FIGS. 5C-5E. The inner mandrel 100 is a variation of themandrel shown in FIG. 5C and FIG. 5F in which the fiber is wrapped ongrooved surfaces on both the radially interior and radially exteriorsurfaces of the inner mandrel 100. All winding surfaces shown are smoothand tapered in the direction of fiber spool out, 112, with the fiberbeing held in place and positioned with the use of athermally-conducting adhesive as described above. Each mandrel 60, 100is independently cooled via coolant inlet ports 102, 104 and outletports 106, 108, which serve to send a recyclable coolant through coolingchannels in the inner mandrel 100 and outer mandrel 60. Chilled ambientenvironment fluid (e.g., water, air) can be routed into the exteriorfiber channel 110 or through the hollow central core 111 for additionalfiber cooling. The exhaust for such coolant, following one pass throughthe spooler 50, is in the trailing direction 112. The exterior mandrel60 may additionally contain passive thermal dissipaters (e.g., radiationpanels) as shown in FIG. 5C and FIG. 5E. The mandrels 60, 100 aresupported at one end only. The fiber is pulled off the free end.

In the design shown in FIG. 5G, up to three single-layer,individually-cooled fiber layers can be combined into a compact spoolerto increase the range of the vehicle. The nested mandrel,actively-cooled spooler concept can be extended to several annularringed mandrels embedded within one another. All fibers are desirablyretained in their grooves by the use of a thermally-conducting adhesiveor similar means that achieves the same intent. For lower poweroperations, multiple wraps can be applied to each winding face, bothinterior and exterior. Each wrap desirably contains an element ofpre-twist to prevent hockling upon pullout during a mission. The fiberfrom one ring layer is desirably passed to the next layer whilemaintaining the maximum possible bend radius on the fiber. Desirably,the trailing edges (not shown) of mandrels 60, 100 should have smooth,polished, radiused surfaces to as to present no sharp edges to thetrailing fiber nor to the cross-wrap fiber leading from one wrappingface to the next.

FIG. 5H shows a cross sectional detail of an embodiment of a drum-typehigh energy fiber spooler such as shown in FIG. 5A. For someapplications, particularly those involving low speed mobility platforms(e.g., underwater and ground vehicles), it will be possible to use adrum spooler on the mobility platform (vehicle). The advantage of a drumspooler is that it simplifies the winding process and does not requireprecision winding and fiber pre-twist to assure a straight pull out asthe mobility platform moves away from the laser power source. It istherefore likely to be less costly than an axial precision-woundspooler. For very high energy transmission, the drum spooler must becooled in a manner analogous to that previously described for an axialspooler. The mandrel 60 will necessarily contain coolant flow channels68, whether interior to the mandrel body or as a bonded set of thermallyconducting flow channels (e.g., a helical tube coil made of copper thatis either soldered to the mandrel 60 or bonded to it with heatconducting material). The coolant that flows through channels 68 can befrom a closed-cycle system that continuously chills the refrigerantwhile dumping the waste heat elsewhere, desirably into a powerconversion system for use onboard the mobility platform. Forapplications where the mobility platform will be working in water orair, either passive or actively forced flow of the ambient fluid (e.g.,water, air) can be passed over and around the exterior of the mandrel 60to further remove heat from the fiber. As with the axial spoolerspreviously described, for ultra-high energy optical power transmissionit is advantageous to have only a single wrap of fiber 62 on the mandrel60. A greater number of wrap layers is possible for lower power levelsor for environments where the ambient environment fluid has significantheat conduction capacity to allow further layers (e.g., ice water fordeep ocean, or sub-glacial lake work). The drum can either passivelyfeed fiber 62 out (possibly with tension maintaining mechanisms) oractively with the use of sensors and servo drives 114 that match therate of fiber pay out to the vehicle forward velocity.

Energy 116 from the base-located laser (not shown) is fed into the drumspooler 38 and the drum spooler 38 unwinds as the mobility platformmoves away from the laser. The fiber 62 from the drum spooler 38terminates at a high energy optical coupler 32 where it enters therotating element 118 of a high power fiber optic rotary joint (FORJ)120.

The FORJ 120 is described in detail hereafter with reference to FIGS.9-10. Briefly, this device allows the optical energy 116 to betransmitted between two adjacent fibers while allowing for one half ofthe FORJ 120 to rotate relative to the other. By this means, the drumspooler 38 may rotate freely without twisting the fiber 62. The outputside of the FORJ 120 leads to a second coupler 32 and fiber section 122that transports the coherent optical energy 116 to the vehicle forfurther use. The drum spooler 38 is supported by bearings 124 on one orboth sides. The bearings 124 are held in place by a drum frame 126 thatis fastened to the body of the mobility platform. Both the drum frame126 and drum sidewalls 128 may have optional internal cooling channelsdepending on the power levels involved. The fiber 62 is preferably abare fiber, since a much greater length can be stored in a given-sizedrum spooler 38, but there is nothing preventing a jacketed fiber to beused, provided the jacket and cladding and any other protective orstrengthening elements have high thermal conductivity. Notably, barefiber always has cladding and almost always has a coating of tens ofmicrons that is not a jacket but nonetheless protects the fiber to adegree.

FIG. 6 depicts an alternative embodiment of the invention wherein thepower spooler 50 resides on the mobile remote system 18. All elements inFIG. 6 are identical to that of FIG. 5B with the exception that thefiber spooler 50 is now mounted on the vehicle. This architecture,wherein massive amounts of optical power are transferred to the vehicleover a fiber optic link over long distances with the vehicle carrying,and laying, its own power line, is the key to enabling a class ofmobile, autonomous systems that could never have previously existedowing to limitations of weight and power generation or storagecapability. As an explicit example, the range (both horizontal distanceand depth rating) of a ship-tethered ROV (industrial class remotelyoperated vehicle) of the type commonly used in the petroleum industry isseverely limited by the excessive size and mass of that electrical-powertether, which grows larger with distance (because higher voltages mustbe used and this then begets further electrical insulation requirements)and is significantly affected by ocean current drag. There are thuspractical limits today to where ROV systems can operate. By contrast, a1 mm diameter jacketed fiber optic laser power tether would scarcely beaffected by currents and the vehicle could receive useful optical poweras far as 100 kilometers from a ship-carried power supply.

In FIG. 7, we explain the first of several high power energy extractionmethods to be employed on the remote system 18 of FIG. 6. The coherentenergy 130 coming from the onboard fiber spooler (not shown) is injectedinto one or more sets of passive or actively controlled beam formingoptics 132 comprising lenses, fiber assemblies, mirrors, prisms, etc,all types of optical manipulating devices. The energy 130 is expandedand directed toward a refractory target 133 such that diffuse laserradiation illuminates a beam dump 134. The beam dump 134 is a bodypreferably made of a refractory material (e.g., beryllium oxide (BeO))that can tolerate sustained high temperature operation. Otherhigh-temperature compatible, highly conductive materials (e.g., certainmetals) could also be used as the beam dump. The core of the beam dump134 is desirably surrounded by an array of thermoelectric converters 136whose interior side contacts with or is exposed to the hot beam dump134. The exterior side of the thermoelectric converters 136 isadvantageously exposed to a cold environment or to a heat sink meansthat is either actively or passively chilled to create the greatesttemperature difference across the thermoelectric converter mechanism.Additional heat exchanger channels 138 may be run through and around thebeam dump 134 to extract heat for further directed use throughout thevehicle or for further power generation by additional thermoelectricarrays or other means.

One such direct heat use for coolant coming through the heat exchangersystem would be that of heating melt water to high temperatures andpressures and using that with a pump 140 to form of a hot water jet forhot water drilling through a thick ice cap—for example thethree-kilometer thick ice cap of Antarctica. Another use would be tosupply hot working fluid through a pump 142 for thermal management of amobility platform (e.g., to keep a planetary robotic rover's mechanismsand science payloads from freezing). The thermoelectric converters 136send electrical power to the onboard control system via a power bus 144,which is regulated by a power management sub-system 146. Electricalpower is subsequently stored in one or more regenerative electricalpower storage means 148 (e.g., a Lithium-ion battery stack, a fuel cellstack, etc.), which serves both as the primary continuous power sourcefor the main onboard computer control processor 150 and controls forperipherals such as the pump actuators 152 that control the hot waterjet pump 140, thermal management pump 142, mobility motors, and thelike. The mobility system is desirably equipped with a sophisticatedsensor network 154 that continuously scans dozens of process sensors156—thermal, pressure, and optical—for overall management of thevehicle.

FIG. 8 shows a physically realizable mobility system power head 160 thatcan receive very large amounts of optical power (e.g., tens of kilowattsto low megawatts) and thence convert and simultaneously direct thatenergy in several useful ways to further the purpose of the mobilityplatform of which it forms the heart. Optical power is delivered to thepower head 160 via fiber 162 from an axial or drum type spooler aspreviously described and located on the mobility platform. The beam isfirst partially expanded via primary beam forming optics 164 and thenvia forward beam forming optics 166 to form a diffuse beam 167 thatimpinges on beam dump 134, thus heating the entire body of the powerhead 160 to high temperature. As previously described, a thermoelectricconverter array 168 may be positioned around the beam dump 134 fordirect generation of electrical power for use on the vehicle. This array168 can be located anywhere around the power head body where heat willbe radiated onto one face of the thermoelectric converter chips (TEC)while a lower temperature surface can be created on the opposite side(e.g., the TEC array could be located either inside the beam dump cavityand cooled on their outward side by heat exchanger channels 176 or bymounting the TEC array on the outside of the beam dump as shown in FIG.7 where it would be chilled by the ambient environment or other externalheat extraction system). A second primary means of direct electricalpower generation is possible by directly impinging the expanded opticalbeam 167 onto an array of photovoltaic cells 170 that are tuned togenerate electricity efficiently at the wavelength of the incident laserradiation. The body of the power head 160, comprising forward housing172 and rear housing 174, can be equipped with internal heat exchangerchannels 176 and heat pump channels 178 that can be used to transportheat to other locations about the vehicle for thermal control in coldenvironments or to power such direct thermal power consumers as hotwater drills and the like.

FIG. 9 shows one embodiment of a high power (e.g., kilowatts to lowmegawatts) FORJ 180 as generally described with reference to FIG. 5A-5H.The housing of the FORJ 180, in this case an axial design, comprises twoconcentric elements: a rotating element 182 that rotates freely and ismounted to the rotating fiber drum (not shown) by flange 184 and a fixedelement 186 that is fixed to the drum holding frame (not shown) and isprevented from rotating by torque arm 188. The rotating element 182 andfixed element 186 together define an optics chamber 195.

Optical power enters the axial FORJ 180 through a first connector 190,which is cooled by coolant that enters at inlet port 192, cools theconnection and exits at outlet 194. However, at this point coolant flowis subsequently routed to housing inlet 196 where it cools the fixedelement 186 and then, by means of a rotary cooling water coupling 198,allows the flow to continue into the rotating element 182 withoutentering into the optics chamber 195. Water temporarily exits therotating member 182 and connects to a cooling inlet 204 of a secondconnector 202, cools the second outlet connector 202, and exits thesecond connector 202 at an outlet port 200 and then re-enters andre-cools the rotating element 182, passes back through the rotary watercoupling 198, passes through the fixed element 186 and then exits toreturn to the cooling system via outlet port 206. Many variations onthis approach are possible, but the concept is to efficiently cool boththe rotating element 182 and fixed element 186 of the FORJ 180 as wellas both fiber connectors 190, 202 using the same coolant system foreconomy. O-ring radial and face seals 208 are used to ensure that waterdoes not enter the optics chamber 195 or optical elements of the FORJ180 nor to leak at any place while advantageously transporting heat awayfrom both housings elements 182, 186.

The rotating element 182 is supported and centered within fixed element186 by bearings 210, which are kept clean and sealed by a shaft seal212. Electric slip ring contacts 214 are used for connector safetyinterlocks and are connected to a safety control system by externalwires (not shown). The purpose of the safety interlocks is to preventaccidental separation of the FORJ 180 while power is on. Additionalsafety sensors comprise a plurality of photodetectors 216 for sensingstray light that might predict the onset of failure of the optics thatwould lead to a catastrophic melt down of the system if left unchecked.Similarly, a temperature sensing network 218 is distributed throughoutthe rotating element 182 and fixed element 186 for the same purpose ofearly detection of a failed optical control system that may be leadingto melt down of the FORJ 180. Similarly, isolated electrical contacts220 for connector integrity lock are provided to ensure both the firstand second connectors 190, 202 are properly inserted and locked inplace.

The optics of the axial FORJ 180 are complex. The incoming beam from thefirst connector 190 will diverge at its end at the fused silica block ata divergence angle defined by its numerical aperture (NA). The divergingbeam is collimated by first collimating optics 222. The beam thentheoretically travels across the evacuated optics chamber 195 andimpinges on second collimating optics 224 where the beam is focused andimpinges on the fused silica block of the second connector 202 where thebeam is injected into the output fiber 203.

Despite the best efforts at precision machining, there will existalignment errors between connectors 190, 202 and their respectivecollimating optics 222, 224. Minor variances in this alignment couldresult in substantial amounts of power being dissipated in the opticschamber 195 and, if left unchecked, could lead to meltdown and loss ofthe device. While fine-tuned optical bench solutions might be developedfor laboratory versions of such a device, that will not be sufficientfor the high power industrial mobility inventions previously describedherein.

To resolve the issues of alignment both due to axial and angular errorsas the rotating element 182 rotates relative to fixed element 186,actuators 226 are affixed to the first and second collimating optics 22,224 for interactively, and with fine precision, moving these respectivelenses in real-time under computer control. Alignment means 226 maycomprise of a plurality of active control elements affixed to each lenssuch that each lens can be both moved in three degrees-of-freedom (e.g.,X, Y, and Z translations) as well as rotated in three degrees of freedom(yaw, pitch, and roll) in order to both actively change both the focuspoint as well as the pointing of each lens.

The connectors 190, 202 will have limited alignment possibility, otherthan that determined by the precision of the concentricity of rotatingand fixed elements 182, 186 and the degree to which fabrication errorsand tolerances permit motion other than rotationally about the commoncenterline. For this reason, the actuators 226 must handle all of thecorrection. The actuators 226 may desirably be arrayed radially aboutthe perimeter of the lens and a minimum of three such elements per lenswould be needed to provide a full six degrees of freedom. Alternatively,the lens could be held by an external servo controlled stage thatallowed for X-, Y-, and Z-translation of the lens while other servoactuators provided for the yaw, pitch and roll orientation. The lensactuator means could employ both slow and fast elements—fast elementsbeing comprised of such technologies as piezoelectric stacks with orwithout displacement amplifiers; MEMS-based actuators for micro-finetuning; acoustic SAW wave linear actuators; electromagnetic and voicecoil type actuators, to name a few. Importantly, these actuators are alldriven by an onboard embedded computer processor that is local to theFORJ 180 or immediately adjacent the FORJ 180 so that each FORJ 180 isindependently responsible for its own real-time alignment. The alignmentcycle begins at low power and a system identification mapping isperformed at specified rotation angles of rotating element 182 relativeto the fixed element 186. At each system identification angle, anoptimization is performed in which the delivered power to the outputconnector is maximized while minimizing the optical and thermal feedbackfrom internal sensor networks 216, 218. The positions of the collimatingelements 222, 224 are then noted and the next angular alignment proceedsautomatically until a full revolution has been logged. A smoothedmapping is then mathematically defined between the discrete calibrationpoints and this mapping then forms the basis for an initial estimate ofthe real-time alignment system at any given angle—the relative rotationangle between the rotating element 182 and fixed element 186 isdetermined by a high precision angular encoder (not shown) that reportsthat angular position to the embedded control system processor. Withthese initial seed alignments as a function of relative rotation anglethe embedded processor then initiates a real-time optimization controlof the collimating alignment motors and actuators for both lenses aspower is ramped up to full industrial levels and the fiber is spooledout from the spooler drum.

FIG. 10 shows another embodiment of an FORJ 180 that can be used withthe present invention: a right-angled, high power FORT 180 in which allelements are the same as for FIG. 9 and further comprises a high poweractively cooled laser mirror 230. The mirror 230 is mechanicallyconnected to highly responsive servo-controlled mirror alignment motorsand actuator means 232 sufficient to control three orthogonaltranslations and three rotations (yaw, pitch, roll) of the mirror 230relative to collimating optics 224, 226. These actuators and motors 232are, as before, connected to the onboard embedded processor which seeksto optimize the amount of optical power being transferred through theFORJ 180 for any given rotation angle. This is in many ways superior tothe pure axial design presented in FIG. 9 in that it allows forextremely fast adjustment of a lightweight, cooled mirror (as opposed toglass optics which have substantially more mass). Furthermore, theaddition of the servo-aligned mirror has the capability to compensatefor translational misalignments between the axes of the assembled FORTconnectors 190, 202. This additional alignment was not possible in theaxial FORJ of FIG. 9 because the relative beam input angles arepre-determined by the machining precision of the connector entries. Inthe FORT 180 of FIG. 10, this machining precision error can becompletely compensated, leading to reduced losses and at higher responsespeed. The same initialization alignment system identification andradial optimization will be conducted, but with the addition of thedegrees of freedom of the mirror added to the optimization algorithm.

FIG. 11 shows an exemplary optical connector 300 suitable for use in thepresent invention. The connector 300 has a fused silica beam expansionblock 302 with a wavelength-specific anti-reflective (AR) coatingcontained inside an optical fiber cable assembly 314 with multi-layerarmored jacket. Because power is lost in the connector 300, watercooling is fed through the connector by water cooling inlet line 308 andwater cooling outlet line 310. The connector is typically equipped witha mating flange 312 for a bolted connection. A dust-intrusion o-ring 316prevents dust particles from entering the optical pathway andpotentially causing a localized thermal buildup by blocking the beam.Two radial contact isolated electrical contacts 318 provide for a testof cable interlock integrity.

FIG. 12 shows the heat engine 160 described with reference to FIG. 8,the heat engine 160 comprising a high temperature housing 320 and aninternal beam dump 176. The laser power enters the heat engine via fiber162 coming from the power spooler (not shown). The beam is expandedthrough primary optics 164 and secondary optics 166 into diffuse beam326, which is directed into refractory beam dump 328. Heat can either betransferred directly through the walls of the beam dump 328 or via anexternal heat exchanger 330 that cycles an effective thermal transferfluid (e.g., liquid sodium) through the beam dump 176 and back into ahigh-power heater 332.

A beta Stirling engine 334 is driven by the heater 332. The engine 334comprises an expansion volume 336, a compression volume 338, a displacer340, a power piston 342, a regenerator 344, and a cooler 346. Theexpansion volume 336 and compression volume 338 are preferably filledwith a working gas, which is typically air or helium. This working gasis sealed within these volumes by the power piston 342 and moved betweenthe hot and cold spaces by a displacer 340. The gas is recycled throughthe cooler 346 and through regenerator 344 prior to re-entering theheater 332. The linkage driving a power piston 342 and displacementpiston 340 will move such that the gas will compress while it is mainlyin the cool compression space and expand while in the hot expansionspace. Because the gas is at a higher temperature in expansion space 336relative to the compression space 338, and therefore at higher pressure,more power is produced by the movement of piston 342 during expansionthan is reabsorbed during compression. This net excess power is theuseful output of the engine. There are no valves or intermittentcombustion, which is the major source of noise in an internal combustionengine. The same working gas is used over and over again, making this asealed, closed-cycle system. All that is added to the system is steadyhigh-temperature heat, and all that is removed from the system islow-temperature (waste) heat and mechanical power. The piston 342 can beused to drive a plurality of electrical generation means. This design,using ultra-high laser-delivered power, forms the basis for a uniquepower generation mechanism that is non-collocated with the source of theenergy.

The power levels being dissipated in heater 332 can range from the lowkilowatt level to a dozen megawatts using a single fiber. Electricalpower conversion efficiencies for a properly designed Stirling enginecan reach thirty percent. A megawatt of laser input power could beconverted to five-hundred horsepower of electrical drive power. Tenmegawatts, feasible with an eight-hundred micron fiber, would yieldfive-thousand horsepower, which is sufficient to run heavy machinery,such as to conducting mining operations eleven kilometers below thesurface of the ocean at the bottom of the Marianas Trench, powered by aship-board diesel power system driving the laser, or to power a fleet ofremotely operated lunar regolith harvesters extracting ice on the Moon,powered by a lunar base nuclear power system using a similar Stirlingconverter to power a laser. Both of these, as well as many other extremeenvironment applications, ideally favor this approach as the cooler 346can easily extract cold from the environment. All of these systems canbe operated at tens of kilometers from a static power base using theapproaches described herein.

FIG. 13 shows a robotic device 348 (a “cryobot”) designed toautonomously penetrate extremely deep glacial ice caps (e.g., theAntarctic ice sheet over Lake Vostok, the South Pole Lake, LakeEllsworth, other such sub-glacial lakes, or even the ice caps of Mars orthe surface ice cap of the Jovian moon Europa) by melting a path aheadof the vehicle as it descends. Prior to this disclosure, no attempt atthe construction of a practical cryobot has succeeded, largely becauseof two factors.

First, prior attempts at using electricity (in a device known as aPhilberth Probe) all failed at slightly over a kilometer of depth. Forpractical reasons—namely, the ice cap freezes behind the probe as itmelts its way down—the vehicle must spool out its connection to thepower source from the vehicle. This requires a large spool of wire onthe vehicle. Because of resistive losses, the voltage must be increasedthe further the vehicle descends until eventually arc-over limits therange.

Second, political restrictions on the use of nuclear power sources inAntarctica. While a small SNAP reactor could power such a device, itwould never be tested in a deep ice cap on Earth.

A laser-powered cryobot, such as the cryobot 348 disclosed in FIG. 13,changes that. Enough fiber can be carried on the vehicle to permit notonly a descent through the deepest known ice caps on Earth—four thousandmeters at Vostok—but also to permit a sample return mission by invertingthe cryobot and melting its way back to the surface.

The advantages of such a system are further enhanced by environmentalrestrictions imposed by the international community regarding entry intosuch subglacial lakes. Planetary Protection restrictions requireextensive testing, certification, and lengthy approvals that can takeyears to decades to approve access using hot water drilling from thesurface, which is the only other known technology that can reach theselakes.

With a cryobot, the vehicle can be sterilized to acceptable levels inthe laboratory, sealed in a sterile container, and inserted into the icecap in a sterile condition. Because the melt hole re-freezes only a fewmeters behind the vehicle, forward contamination is prevented.

The design of a cryobot is governed almost entirely by the diameter ofthe vehicle and the desired descent rate through the ice. This, alongwith the temperature of the ice, determines the input powerrequirements. For example, a one-quarter meter diameter by two-meterlong cylindrical cryobot with hemispherical end caps, similar to thecryobot 348 depicted in FIG. 13, working in ice with a temperature ofminus five degrees (C.) will descend at a rate of fifteen to twentymeters per day when powered by a five-kilowatt fiber laser. Doubling thediameter (e.g., to accommodate larger science payloads) will reduce thedescent rate by a factor of four under the same input power.

FIG. 13 discloses one embodiment of a viable, deep ice cryobot 348having a cylindrical shell 350 with hemispherical ends. Power isdelivered via a bare optical power fiber 352 to the rear (top) of thevehicle. Data may be modulated and extracted via the power fiber 352 sothat a surface-based mission control center could maintain ahigh-bandwidth data link with the cryobot 348 throughout the mission.The cryobot 348 may be equipped with an auxiliary (second) co-linearaxial spooler 354 having an auxiliary fiber of smaller diameter than thepower fiber 352 for the purposes of maintaining a dedicatedcommunications link. This is of considerable value for the purposes ofsupervised autonomy in which a surfaced-based scientific or industrialteam could interpret real-time data and override local autonomousbehavior code for such purposes as collecting a sample from the adjacentice column or for potentially causing the vehicle to deviate from adirect vertical descent. A primary power fiber spooler 356 is surroundedby actively-controlled chill water heat exchangers 358 that melt waterfrom the front of the vehicle. When a cryobot melts through an ice cap,the bubble of water that surrounds it sees the hydrostatic pressure ofthe ice mass above it, such that by the time it penetrates a sub-glaciallake at, say, four kilometers depth, all of the sealed components withinthe vehicle will see four hundred bar (forty MPa) applied externalpressure. The design must therefore include provision for eitherstructurally resisting that pressure or for allowing compliantequalization of pressure (through the use of oil filling and a compliantaccumulator). Pressure housing 360 houses the primary onboard controlcomputer, and guidance, navigation, and thermal management electronics.Its temperature is maintained within a functional band by heat exchanger362.

A science or sample bay resides at the center of the vehicle and caninclude, among many possibilities, water sampling pumps 364; watersampling router valves 366; a lateral ice wall sampling system 368; alateral ice wall imaging system 370; and potentially a lake floorsediment sampling system. Preferably, the cryobot 348 includes one ormore regenerative power storage systems 372. A pump 374 provides bothheated and chilled water as needed to the various heat exchangersthroughout the vehicle. Science sample carousel 376 can be used forstorage of a score or more of filtered water samples. A high-pressurejet pump 378 draws hot water from hot water heat exchangers 380 anddrives the heated water through hot water first stage jet feed lines 382to hot water jets 384 located at the nose of the vehicle. Selectivetransfer of hot water to different jets (there may be as many as needed)for the purpose of auxiliary or primary steering of the vehicle for thepurpose of obstacle avoidance maneuvering. Melt head actuators 386provide primary or auxiliary steering of the melt head, also for thepurpose of obstacle avoidance maneuvering.

As previously discussed, optical power reaches the refractory melt headvia fiber and passes into a melt head housing 388 through a fiberjunction block 390 and primary and secondary optics 392, 394 thatdiffuse the beam and cause it to impinge uniformly on a beam dump 396,where it heats the refractory material 398 to high temperature.Electrical power can be extracted in several ways, the most effectivefor this low power (electrical) operation being a thermoelectric array400 that takes advantage of the exterior cold (melt water) environment.

Importantly, the nose of the vehicle contains a synthetic aperture radar(SAR) 402 antenna (the electronics for which are located in the pressurehousing 360) that is tuned to one or more frequencies (operatedindependently or synchronously) optimally chosen for penetration of ice.Because of the relatively slow, uniform rate of descent, it is possibleusing SAR to build a high resolution map of what is ahead of the vehicle(including both liquid voids and solid objects) and to take appropriateevasive action to avoid those features if necessary. This behavior canbe programmed as a robotic function onboard the vehicle and can operatewithout human intervention. In order for the SAR system to operate, thematerial of the beam dump and melt head material 398 must be made of aradar-transparent material. A suitable example, which is also arefractory material, is beryllium oxide. The front of the vehicleadvantageously also contains a miniature, pressure-proof fiber video orstill camera 404 for the purposes of documenting the ice in front of themelt head. Fiber cam illumination may include pressure proof array ofhigh intensity LEDs 406 or other compact illumination source.

FIG. 14 shows the field setup for a laser-powered cryobot mission. Ahigh power fiber laser 408 is electrically operated through powersupplied by a diesel generator 410. The diesel generator 410 alsoprovides electrical power for operation of a pumped chill water coolantsystem 412, which provides chilled water for thermal control of fiberlaser 408. A high power in-line coupler 414 connects laser 408 to amodular high power process fiber 416, which carries the laser energyover land over some intermediate distance (preferably as short aspossible) to provide flexibility in the location of the laser powergeneration source away from the cryobot injection point into glacier418. At the injection point, a melt hole entry cab 420 serves to lowerthe cryobot 348 into the glacier during the initial insertion until thevehicle is submerged into a hole, which is pre-melted so that liquidwater is available for system cooling. The entry cab 420 also contains ahigh power laser fiber coupler 422 that allows the vehicle to betransported to the entry melt hole in a modular fashion, independent ofthe surface segment of the laser transmission system. The cryobot 348 isalso equipped with a high power laser fiber coupler 424 at the melthead. This allows the high power laser fiber spooler 356 to be modularlyreplaced in the field.

FIG. 15 shows a detailed system schematic for a physically-realizablecryobot capable of reaching the South Pole Lake (located twenty-eighthundred meters directly beneath the United States scientific outpost atthe south pole) in thirty days, descending through the lake to itsbottom, changing its attitude to that of a horizontally-oriented AUV,collecting a sediment sample from the bottom of the lake, and theninverting to a melt-head-up orientation, making itself positivelybuoyant, and thereby allowing it to melt its way back up through the icecap in a similar thirty-day egress mission. The objective is to providethe sediment sample return without the use of hot water drills.

The surface segment consists of two one-hundred kilowatt dieselgenerators 426 that supply three twenty-kilowatt fiber lasers 428. Theoutput of each twenty-kW laser is fed to a matched coupler 430 throughan approximately three-hundred micron diameter bare fiber core 432.Approximately eight kilometers of this bare transmission fiber arewrapped on high power fiber spooler 434, which resides inside the tailcone of the cryobot. Laser input power from the fiber 432 is fed intobeam forming optics 436 where the beam is expanded into beam dump 438that is surrounded by thermoelectric converter arrays 440. The impingingbeam 442 could, contrarily, be focused to create a stable plasma in aworking gas at the center of the refractory thermal flywheel. The resultis the same: the conversion of coherent laser energy into radiant heat.This heat is extracted directly for mechanical tasks by heat exchanger444 and this hot water may be both used to control other parts of thevehicle using thermal management pumps 446 that can be made to pump bothheated and cold melt water to locations where needed. The hot water fromheat exchanger 444 is also desirably sent directly to high pressurepumps 448, where it can be directed to hot water jets for the purpose ofenhancing the rate of vehicle descent.

The raw electrical power generated by arrays 440 is fed through powerbus 450 to a series of power management modules 452 with redundantelements present to provide increased mission assurance. Regulated powerfrom modules 452 is sent to regenerative power storage means 454, whichcan store power in the form of lithium-ion batteries, fuel, cells andthe like. These electrical power storage systems provide the standardpower bus for all cryobot onboard systems.

The main system executive resides on computational processor 456, whichin turn communicates with the surface via data conversion switch 458that converts electrical data communications impulses into lightimpulses which are then fed into communications fiber spooler 460 whichcontains eight or more kilometers of smaller diameter fiber 462 thanthat used for power transmission. This is then re-converted to a digitalsignal on the surface via converter box 464 (e.g., a fiber optic toEthernet switch) and thus provides a common data feed to mission control466 for monitoring and control of the mission.

The main processor 456 also communicates with a real-time vehicle sensornet 468 that reads scores of environmental state sensors 470 (e.g.,thermal, pressure, optical) that are used to provide input into thevehicle thermal management and safety override sub-systems. Theprocessor 456 also communicates and controls the Trajectory Diversionand Attitude Control System, which is composed of a flux gate compass472; vehicle roll sensor 474; vehicle pitch sensor 476; melt head pitchsensor 478 and actuators: longitudinal center of gravity shifter 480;radial center of gravity shifter 482; and melt head pitch drives 484.These systems and sensors allow the vehicle to not only allow deviationof the vehicle trajectory from a direct, gravity-driven vertical descentthrough the ice, but also permit the vehicle to fully invert—a processthat takes time, but is feasible with the stated systems for moving thevehicle mass centroid to an eccentric position. This allows for enhancedobstacle avoidance and also a sample return or abort to surface.

The vehicle contains an auto-egress system that works in conjunctionwith the center-of-gravity shifters. This includes a variable buoyancyengine 486; an emergency ballast drop system 488; and an “ice tractor”system 490. The cryobot begins its mission in a head down position (asshown in FIGS. 13-14) and maintains this orientation, assuming noobstacle avoidance is required, until it reaches a sub-glacial lake. Itthen uses the longitudinal center-of-gravity shifter 474 to cause thevehicle to rotate ninety degrees up to a horizontal attitude; the radialcenter-of-gravity shifter 476 allows the vehicle to roll to a preferredpointing direction so that formerly lateral-looking science payloadsensors can be made to look directly at the lake bottom. The variablebuoyancy engine 486 can be used to cause the vehicle to descend andhover at a specified altitude over the lake floor while a sediment coresample is taken. The complete science payload can contain, for example,imaging systems 492; environmental sensors 494; lake bottom sedimentcore sampler 496; lake bottom sonar profiler 498; and water samplers,including filter samplers 500.

At the conclusion of the data collection phase of a mission (and theacquisition of the desired core and water samples) the variable buoyancyengine 486 is caused to dump ballast (sterile water). Thecenter-of-gravity shifters invert the vehicle to a head up position andthe vehicle begins to melt its way upward, using the positive buoyancyof the vehicle to drive it upward in a bubble of water. An optional,emergency ballast drop-weight (made of a neutral, non-corroding, sterilematerial) system 488 may be activated if there is a failure in thevariable buoyancy system 486 fails on ascent. Lastly, an optional “icetractor” 490 can be employed to assist in ascent by providing aratcheting mechanism that allows the vehicle to mechanically forceitself forward (i.e., upward). This can comprise direct lateral spurgears that can be extended from the body of the cryobot and driveneither by pumped water or electrical motors or it could be of a formconsisting of a temporary lateral locking mechanism (e.g. a pressurecylinder and blade pressed against the ice laterally) and atranslational ratchet that advances a specified distance up the body ofthe vehicle, locks to the wall (using a similar lateral forceapplication mechanism means) and then releases the lower latch and adraw motor (e.g. a linear actuator, or gear driven linear track means)pulls the vehicle forward. The intent of the ice tractor 490 is tomaintain contact between the melt head and the advancing ice column.

Importantly, the vehicle also contains an Obstacle Avoidance andNavigation System, which contains a forward-looking ice-penetrating lowfrequency radar (e.g., 100 MHz) 502; a forward looking mid-frequency icepenetrating radar (e.g., 400 MHz) 504; a depth sensor 506; a highprecision gravimeter 508; and an odometer 510. The ice-penetrating radar(IPR) system forms a part of the SAR system previously described and canbe used to dramatically enhance the ability of the vehicle to detectlarge objects as far as a kilometer ahead of the vehicle and small(centimeter-scale) objects as far as fifty meters ahead of the vehicle.Further, for Arctic and Antarctic operations on Earth, the top roughlyfifty to one-hundred meters of ice is not solid. This is a transitionzone between fresh, loose snow and solid ice known as the “firm” layer.Because it is not made of solid ice, a cryobot returning to the surfaceusing positive buoyancy will eventually not be able to cause the vehicleto rise to the surface because air content in the firm will cause abubble of air to form at the head of the vehicle. The ice tractor 490will overcome some of this and a cryobot of the type described here willbe able to rise to within fifty meters of the surface before bothbuoyancy and lateral ability to hold load will fail. At this point asurface-based recovery procedure is needed that employs a hot waterdrill to penetrate to the vehicle. An auto-docking and latching systemcan be created to retrieve the vehicle at that point. Knowing where todrill, however, is a critical part of this recovery procedure and forthis the SAR radar now is used as a directional beacon for the drillingsystem.

FIG. 16 shows another embodiment of the invention in which a laser powergeneration system 512, residing on a planetary lander system, is used toremotely power an exploration and science rover 514. The advantages ofthis approach are significant in that the rover 514 can be made muchmore lightweight and agile—and therefore survivable—in a rugged, unknownenvironment. Furthermore, it allows for the costly, heavy powergeneration equipment to remain with the lander (or planetary base) andtherefore reduce the risk of losing that precious resource were there tobe an accident with the rover 514. This approach can be used to eitherpower multiple rovers from the same power source or to allow many longrange missions by a single rover. The concept can be further extended toone in which a fixed planetary base—for example, a lunar polar base in adeep, sun-less cold crater mining water ice—can use a common centralplanetary (nuclear) power supply generating power in the five-hundredkilowatt to multi-megawatt range to operate a remote, distributed fleetof large industrial regolith harvesters that scoop up the surface dustand extract water through direct heating.

The planetary lander laser power system 512 generally comprises theelements previously described. The power supply 516 for laser 518 ispreferably provided by a compact radiothermal generator (RTG) forlightweight initial robotic missions or a planetary high power (nuclearfission) thermal source for industrial operations, either of which aresubsequently converted to electrical power using any of the meanspreviously described and then used to drive the laser. Photovoltaicscould also be used to provide power but this is not an option for outerplanet exploration and resource extraction (due to insufficient solarflux).

The mobility system 520 comprises the common power train previouslydescribed, which includes a rover-based fiber spooler system 522 thatreceives laser energy via inlet fiber 524, which is trailed out behindthe vehicle as it moves from onboard fiber spool 526. The fiber spool526 is cooled by actively controlled heat exchanger and chiller 528 andpassive heat dissipation system 530. A high power fiber coupler 532allows connection of a beam dump 534 via process fiber 536.Thermoelectric arrays (or other electrical power generation meanspreviously described) send electrical power via power bus 538 to a powermanagement system 540 which charges or recycles a regenerative energystorage system 542. Direct controlled power from the regenerative powerstorage system 542 can be delivered at high current capacity toindividual motor or actuator controllers 544 that can be used to drivediscrete wheel drive electric motors 546 via power bus 547. Onboardcomputer system 548 makes behavioral decisions either autonomously orscripted and sends digital control signals via digital links 550 tooperate the discrete motor or actuator controllers 544. All systemscomposing rover mobility system 520 are carried onboard the actual rover514.

FIG. 17 depicts another direct variation of the invention in which anunmanned underwater vehicle receives power in a directly analogousfashion as that described in FIG. 16. There are two noteworthydifferences in FIG. 17 vis-a-vis FIG. 16. First, the laser and laserpower supply are based on a floating platform (e.g., an offshore oil rigor complex) or a ship as part of a ship-based power system 552. Eithermission-specific, dedicated diesel-electric power can be provided or theonboard power plant for the ship or platform itself (likely eitherdiesel or nuclear) can be used to provide an essentially unlimitedamount of input power to the laser. This is an important factor as itpermits (unlike an RTG-powered planetary lander, for example) industrialpower levels to be optically transmitted to the underwater vehicle. Forthe same reasons as discussed earlier, there are severe limits to theamount of power an electrically operated underwater vehicle can receivefrom the surface. The design of a high powered ROV for work at threekilometers depth, for example, is a complicated undertaking and themanagement of the cable alone is a major logistical cost and seriousburden which limits the class of ship that can be used to conduct thework. While there are line losses associated with laser powertransmission (see FIG. 1B), and further losses associated withconversion of the delivered energy into electrical power, those arerelatively small issues where there is plentiful electrical power on thesurface. The laser-powered AUV 554 or ROV can competitively be operatedagainst the mechanically inefficient current state of industrial ROVsbeing used for the offshore oil industry. Further, with thelaser-powered approach shown in FIG. 17, it becomes realisticallyfeasible to conduct high power industrial operations anywhere under theocean, to full ocean depth (eleven kilometers).

The mechanism for power conversion for underwater vehicle applicationsshown in FIG. 17 will likely be a heat engine (e.g., Stirling cycle) asthis can be efficiently, and economically scaled to very large,continuous power levels (thousands of horsepower). Unlike the planetaryrobotic landers, regenerative electrical power storage systems 542 willlargely be for clean (low electrical noise) operation of onboardcontrol, sensing, and communication and for limited emergencymaneuvering. The actuators (e.g., main thrusters 556) will be driven viapower bus 545 directly from the electrical power output (generator)driven by the heat engine. The architecture shown in FIG. 17 creates anentirely new design space for underwater vehicles. Because the powerfiber can be very small in diameter (e.g., one megawatt through aneight-hundred micron fiber) and because the vehicle has control of itsown trajectory (because of the onboard fiber spooler), it becomeslogical to run not only traditional surface-controlled ROVs, but alsoAUVs with this method, regardless of the degree of human interventionwith a preprogrammed mission that may be carried out autonomously inthese last two cases. The ability to ditch the majority of the vehiclebatteries means less requirement for expensive syntactic (ocean depthrated floatation foam) and the entire vehicle becomes able to be reducedto its key functions of high power mobility and its designated missiontask (e.g. repairing a deep pipeline; harvesting manganese nuggets offthe deep ocean floor, etc.).

A dramatic variation of the invention is shown in FIGS. 18-20. Fornearly three decades, intense research has been conducted on the subjectof laser or microwave powered launch of spacecraft from the ground toLow Earth Orbit (LEO). These concepts involve direct beaming of a laser,or banks of lasers, at a target launch vehicle in order to eitherdirectly ablate an expendable material on the back side of thespacecraft to create thrust or to heat a working fluid within thevehicle, generally using mirrors on the periphery of the vehicle toreflect the light towards a reaction chamber where the working fluid isto be heated, and then expand the working fluid through a nozzle tocreate thrust. Regardless of the method chosen, all of the approachesthus far attempted with laser launch have failed for three primaryreasons: atmospheric attenuation of the beam; atmospheric distortion ofthe beam; and line-of-sight limitations. For an object to reach a stableorbit in LEO, it must reach an altitude of approximately three-hundredkilometers or more, but more importantly, it must accelerate to atangential velocity of approximately eight kilometers per second. Thelaunch trajectory is thus curved and carries the vehicle a substantialdistance horizontally away from the launch site before orbital insertionparameters are met. Tracking of the vehicle and attempting to keep thebeam locked onto it becomes a daunting task. Schemes have been proposedto have multiple beaming stations around the Earth to deal with theproblem of not being able to keep a single beam locked onto an ascendingvehicle when it goes over the horizon, but these would representwasteful duplication of expensive laser power generation systems.Similar drawbacks apply to microwave power beaming. Both approaches aresignificantly degraded by weather.

FIG. 18 presents the generic concept of fiber laser launch. Similar tothe previous discussions, a ground-based laser power generation station558 provides very large amounts of power into fiber 560, which isspooled out from a launch vehicle 562. The ground station consists ofpower source 516; laser chilling station 564; laser 518; high energyprocess fiber 566; and inline couplers 568. A spooler 570 on the launchvehicle 562 is chilled by any of the means previously identified, but inthe case of laser launch an additional coolant could be in the form of acryogenic working fluid (e.g., liquid hydrogen, liquid nitrogen) that isstored in chamber 572 and fed regeneratively via channels 574 through aheat exchanger through fiber spooler 570 to pre-heat the working fluidbefore entry into the working fluid injection ports 576 into a gasexpansion chamber 577. Importantly, the output of spooler 570 goesthrough an optional coupler 578 and is then connected to a laserinjection interface structure 580 by fiber 582 where the output proceedsthrough beam forming optics 584, 586.

There are two general approaches available at this point to createthrust, both of them efficient. In the first idea, the beam formingoptics 586 focus the beam 588 of laser energy through a laser window 590on the back side of the gas expansion chamber 577 and bring the beam toa point inside the gas expansion chamber 577, creating a stable centralplasma core 592. Working fluid enters the gas expansion chamber 577 viafluid injection port 576 or other entry means. The working fluid can beany molecule that forms an expansive gas when heated—thus it could becryogenic liquids (e.g., liquid nitrogen, liquid hydrogen, liquid air,liquid argon, CO₂, etc.), compressed gases of any type (e.g., nitrogen,xenon, hydrogen, argon, air etc.), or liquids of any type (e.g., water,methanol, or the like that, when heated, dramatically expands in itsgaseous phase).

As the working fluid enters the gas expansion chamber 577, it ispreheated in the focusing zone or optically heated expansion cavity 594and begins to expand, passing around the central plasma core 592 viapath 596. A convective mixing zone 598 exists beyond the plasma centroid592 and at this point the hot, expanded gas passes through nozzle throat600, through high temperature expansion nozzle 602 and creates thrust624. Alternatively, plasma core 592 can be replaced by a series of heatexchangers where an expanded (as opposed to focused) beam impinges, withall other facets remaining the same. The purpose of the heat exchangeris to impart the energy of the beam into the working fluid, rapidlycreating superheated gas in reaction chamber 577 whereupon, as before,the gas is expanded through nozzle throat 600 and into high temperatureexpansion nozzle 602 (i.e., exhaust) creating thrust 624. It is thepurpose of the method described to emulate the manner in which a normalmono- and bi-propellant rocket engine creates thrust, but importantlyallowing the use of inert fuels (working fluids) which will lead to muchsafer launch and operation—unlike traditional rocket launch, thetermination of the laser beam would immediately cease thrust and therewould be no danger of an exploding booster should a guidance system failduring launch. The reaction chamber or gas expansion chamber 577 isdesirably designed to minimize radiative heat loss through the chamberwalls 606.

Importantly, the working fluid can be from several sources. Duringinitial flight through the atmosphere, a ram air scoop 608 in the openposition on the side of the vehicle allows atmospheric air 610 to becompressed and taken into the vehicle. This atmospheric air 610 can thenbe sent through a ram air intake structure 612 and through flow selectormeans 614, and through bypass valves 616. Bypass valves 616 canoptionally send the working fluid to the heat exchanger located in thefiber spooler 570 for preheating to improve the efficiency of use of allheat being delivered to the vehicle via the fiber laser power system. Atapproximately twenty to thirty kilometers altitude, the atmosphere willbe too thin to provide effective quantities of working fluid to beexpanded to create thrust. A gradual transition will take place, whereworking fluid may be drawn both from the atmosphere as well as from thechamber 572. Eventually, at sufficient altitude, classed as“exo-atmospheric” flight, the vehicle 562 will need to rely solely onstored onboard working fluid (i.e., propellant). Chamber 572 carriesthat exo-atmospheric working fluid, which is preferably one of liquidhydrogen, liquid nitrogen or other liquefied gas, but alternativelycould be a stable fluid such as water and other liquids and compressedgases (see above) as well as traditional monopropellants used forspacecraft maneuvering. The logic for using liquid water is that themost logical micro payload (the class of launch vehicle most likely tobe powered by this concept in the one to one-hundred kilogram payloadrange) is, in fact, water because it is a dense,acceleration-insensitive material that is of great demand in low earthorbit (LEO). Other payloads might include dense consumables andacceleration resistant electronics, sensors, and other high-technologyre-supply items that may be needed in LEO. The working fluid containedin chamber 572 can be forced into the gas expansion chamber 577 byseveral means, including vehicle acceleration; an optional turbopump617; or an optional gas blow down system 618 that utilizes an inertpressurized gas to force the fluid through channel 620 to the reactionchamber (i.e., gas expansion chamber 577).

The length of optical fiber needed to achieve orbit is variable as thelaunch vehicle can carry an independent small propulsion and guidancesystem for final orbital insertion. From a practical standpoint,however, a fiber length on the order of one-hundred kilometers could beconsidered a limiting value as attenuation along the length of the fiberwill eventually reduce the effective power received at the vehicle.During the highly energetic initial phase of the launch, a properlydesigned vehicle should be able to make use of the majority of the heatdelivered as the power loss over the fiber deployed behind the vehiclewill be small. Regenerative pre-heating of the working fluid, usingchannels 574, represents one of several means for extracting heat bothfrom the coherent or focused element of the delivered laser energy (viathe beam focusing optics) and from the power dissipated in the fiberspooler 570. The spooler 570 could advantageously be placed within theworking fluid flow path or reservoir prior to the fluid being injectedinto the focusing zone or optically heated expansion cavity 594. Bothsources (coherent optical and non-coherent radiative heat from thespooler) will viably contribute to the overall thrust of the system.

Because the objective of fiber laser launch is to dramatically reducethe cost of placing small kilogram-level payloads (1 to 100 kg) intoLEO, the vehicle design must be as efficient as possible. Thus, measuressuch as using the lightest weight materials for the vehicle structureand propulsion and guidance systems and striving for economy of scaleare important. An important facet of economy will be that of fiberrecovery. A one-hundred kilometer bare optical fiber will cost, in 2010dollars, between twenty and thirty thousand dollars depending on itscharacteristics and core diameter. This price may be reducedsignificantly with large quantity purchases and improvements inlong-fiber extrusion manufacturing techniques. Nonetheless, it willremain essential for commercial launch operations to reuse that fiber asmany times as possible. A bare one-hundred kilometer fiber extended in atypical parabolic launch trajectory will take a substantial time to fallthrough the atmosphere (on the order of more than an hour from thehighest point) owing to its small diameter and low descent terminalvelocity. A large, servo-controlled drum spooler 622 can be used toengage the fiber immediately after launch and reel the fiber back inbefore it can hit the ground. The physics for this are well within thelimits of current mechanical systems design and available materials. Thedrum spooler 622 is not used during launch; it is strictly used forretrieval of the fiber after launch and does not engage nor wrap any ofthe launch fiber until it has been fully spooled out by the launchvehicle. In the notional example shown in FIG. 18, the high power fiber566 coming from the laser 518 can be advantageously latched to drum 622at high energy connector 624, which mates to connector 626 which isrigidly affixed to drum 622. Following a launch, connector 626 can bedisconnected from connector 624 and the drum 622 will be free to beginthe fiber retrieval process. With proper design, the fiber can bepost-processed, cleaned, and re-wound for a subsequent series oflaunches.

FIG. 19 shows an embodiment in which one or more fiber spoolerassemblies 628 reside on the centerline of the launch vehicle. The fiber630 connected to the laser source not shown is protected by fiber guide632, which protects the fiber 630 from direct thruster plume impingementthat might otherwise damage the fiber 630. The fiber 634 from theinboard side of the fiber spooler 628 connects to high power fast rotarybeam switch assembly 636 at its centerline. The beam is expanded throughoptical system 638 whereupon the beam impinges on the high speed indexedrotary mirror 640 at the switch centerline. Servo motor 642 is connectedto a high speed, high stiffness rotary shaft 644, the rotationalposition of which is sensed by embedded rotational encoders. Therotation of shaft 644 causes high speed indexed rotary mirror 640 todirect the coherent laser energy to a plurality of fixed, static mirrors646 and 656 arrayed radially around the central high speed indexedrotary mirror 640. When the beam is directed to the fixed, static mirror646, the fixed, static mirror causes the laser energy 648 to bedeflected to beam focusing optics 650, which in turn inject the beaminto coupler 652 for subsequent transmission to thruster 654. If highspeed indexed rotary mirror 640 is subsequently rotated until it alignswith high energy fixed, static mirror 656, the beam is then diverted toexit fiber 658, which carries the optical energy to thruster assembly660. The light enters thruster assembly 660 via laser optics cavity 662,where the beam is either focused or defocused as previously discussed(with reference to FIG. 18) for the purpose of optimal heating of heatexchanger or plasma cavity 664. Working fluid 666 enters heat exchanger664 and is subsequently heated and expanded through nozzle 668 to createthrust 670. In this fashion any number of axially centered fiberspoolers can deliver power to a radial array of thrusters.Advantageously, as will be described below, three or more thrustersequally distributed radially (for example, three thrusters would haveone-hundred twenty degrees of angular spacing between them relative tothe launch vehicle centerline) allow for a significant simplification ofthe vehicle while still enabling full thrust vector control duringlaunch.

Thrusters 654, 660 are advantageously canted at a desired divergenceangle 672 from centerline so as to further reduce the possibility ofimpingement of the exhaust plume from these thrusters with the trailingfiber. Further, by canting the thrusters 654, 660 and using three ormore thrusters, it is possible to achieve active thrust vectoring of thelaunch vehicle with no moving parts associated with the thrusters 654,660. The high power fast rotary beam switch assembly 636 is capable ofrapidly transferring power to a specific thruster based on a desiredvehicle direction. For direct, straight ascent, the laser is rapidlyshifted between thrusters so that all thrusters receive equal amounts ofpower and, therefore, each nominally produces symmetric thrust and thevehicle will maintain the instant tangent trajectory that it was on.However, even with dissimilar (or physically identical but variablyperforming) thrusters, an onboard computer control system can rapidlygenerate a real-time vehicle state vector matrix and from that determinewhich thruster to favor in order to divert the vehicle to the desiredtrajectory.

FIG. 20 shows another preferred embodiment of the fiber laser launchconcept. In this variant, a plurality of fiber spoolers 674 arrayed in aradial fashion about the centerline of the vehicle delivers power to aseries of laser injection systems or assemblies 676. A high energy barefiber 678 trails behind the vehicle during launch and connects to aground-based laser (not shown). Fiber guides 680 protect the trailingfibers from direct exhaust plume impingement from the thruster. Thespoolers 674 are connected via fiber 682 to actively cooled high powercouplers 684, which inject the beam into the laser optics cavity 686 vialaser injection assemblies 676. Beam forming optics 687 contained ineach injection assembly 676 are independently controlled in real-time toprovide either a focused or diffuse output into the heat exchanger orplasma zone 688 at the core of the laser optics cavity 686 wherein aworking fluid, injected at port 690 is superheated and expands throughexpansion nozzle 692 to create thrust 694. In this embodiment, one ormore thrusters 696 are centrally located either on centerline or arrayedsymmetrically, radially, or otherwise about the vehicle centerline so asto create a central thrust capability. One or more of these thrustersmay be additionally gimbaled so that its thrust vector can be modifiedunder real-time computer control to maintain the vehicle on a desiredascent trajectory.

Notably, hybrid variants of the inventions described in FIGS. 18-20 arepossible in which fast beam switches and beam splitters are used tocombine many laser inputs and channel them to many thruster outputs.These techniques can be used to boost larger payloads. Telemetry fromthe vehicle to the ground, or conversely from radar tracking of theascent vehicle, can be used to determine the instant state vector forthe launch vehicle. This can be used as the basis of correctivealgorithms for steering the vehicle back to a correct course. Thevehicle can optionally have onboard a navigation system consisting ofeither purely inertial sensors, a GPS (global positioning system)receiver, or other methods for estimating the position of the vehicle atany point in time and that information can be sent back in real-time toa mission control computer either via radio (RF) telemetry or viamodulated data signal superimposed on the laser power transmissionfiber. This technique advantageously eliminates several systems from themass of the launch vehicle and it allows for direct non-line-of-sightcommunications to the vehicle, possibly for over-ride of the onboardtrajectory control or for range-safety termination of the launch.

Another variation on fiber laser launch is that of an intelligentautonomous battlefield delivery system. This is far more effective than,e.g., a GPS-guided artillery shell for several reasons. First, the rangefor a laser-powered payload is in excess of one-hundred kilometers andmore likely on the order of two-hundred kilometers given that realisticfiber spoolers can be up to one-hundred kilometers long and, if thepayload separates at apogee, then it will ballistically coastapproximately that same distance. However, up until the point of fiberseparation it will be possible, again via modulated data on the powerfiber, or on a dedicated separately spooled fiber, to communicate withthe payload and to cause it to be re-directed. A forward scouting teamcould provide such a system with real-time GPS coordinates (even ifmoving), which could be uploaded to the payload for real-timere-targeting. Further, there is no requirement for a maximum thrustflight nor for a ballistic trajectory. The fiber laser launch conceptpermits flight down to minimum stable flight speed as well as“loitering” in a vicinity—made possible because the power source iscontinuous and substantial, and located at a rear base of operations.This means that the flight vehicle's dwell (or “loiter”) time in an areaof operations could be made indefinite and the vehicle would not berequired to carry with it any fuel (because at low altitude, atmosphericair can be the “working fluid” for propulsion). Because the flight speedcan be made variable, and arbitrarily low if needed, sensitive suppliescould also be sent to a forward operations team (human) with precisiondelivery capability.

FIG. 21 shows another variation of the invention in which a rotary beamswitch 698 is placed between the laser source 518 and an array of two ormore spoolers 700, 702. These spoolers 700, 702 are advantageouslylocated on docking ports adjacent the central power supply and laserfacility 704 such that a mobile autonomous vehicle 706 could returnautomatically following a mission (after having expended its one-usespooler) and dock with a port containing a full spooler. At that pointthe vehicle 706 could re-load a fresh spooler by removing it from thedocking port and latching it onto a receiver port on the mobility system708, thus re-enabling it for another mission.

As an example, the mobility system 708 would begin a mission using fiberspooler 702 which, as previously explained, is connected to a powerconversion system 710, which generates electrical power or alternativepower to cause the mobility system 708 to move. At the conclusion of amission, mobility system 708 returns to the central power laser source704 and discards spooler 702 and, while operating on residual onboardelectrical power storage systems, moves to the docking port thatcontains a second spooler 700. It then acquires that spooler 700,connects to it, and notifies the laser that power can now be transmittedthrough that spooler. The main computer system at the laser source 704then causes beam switch 698 to re-route the laser energy to the portthat connects the power to spooler 700 with fiber 712. This is a viablemulti-mission-enabling design that permits re-load of a single vehicle(e.g., a planetary robotic exploration vehicle returning to a lander)for subsequent missions while maintaining the heavy elements of thesystem (power source and laser) on the lander. However, this sameapproach can also be used to sequentially send power to a plurality ofmobility systems (e.g., autonomous ground vehicles on a battlefield orforming a defensive perimeter around a forward base of operations).

Variations of this same theme are possible in which the mobilityplatform 708 carries multiple fiber spools and can autonomously connectto an available laser power docking station which contains anappropriate high power laser coupler. In this fashion, the vehicle couldutilize the presence of multiple laser power sources and transfer fromone to another while still having an operational radius with respect toeach laser power source. An example of a situation where this may proveadvantageous would be the exploration of the Ross Ice Shelf inAntarctica, where a surface-based traverse vehicle could carry a singlelaser source to a new location at the limit of the fiber spooler carriedby the vehicle. By drilling a new access shaft and lowering a new lasercoupler, the vehicle—temporarily operating on onboard stored power—couldrendezvous and dock with the new coupler, activating a fresh spool offiber carried by the vehicle, and, hence, begin a new period ofexploration relative to the new location of the laser power source.Another application of the present invention contemplates a small arrayof such laser power stations located on floating buoys in the ocean witharmored fiber cables carrying the beam to subsea docking stationswherein an underwater vehicle (autonomous or manned) could dock with thecoupler and, using a new vehicle-carried spooler, continue on a newjourney of science and exploration.

FIG. 22 presents another embodiment in which a remote mobility system714 (which will be explained within the context of an unmanned aerialvehicle but it could also be an unmanned ground vehicle system,underwater system, or a manned variant of any of those) again receivescoherent laser energy, generated by a forward base power system 716comprising a power generation system 516 and a laser cooling system 564connected by cooling and power delivery channels to a high power fiberlaser 518; high power delivery fiber 566 and leading to fiber coupler568. Bare fiber 718 from an on-vehicle spooler 720 trails out throughfiber pay-out guard 722, which prevents the trailing fiber 718 frombeing damaged by vehicle locomotion means. The fiber spooler 720contains, as previously described, a spool 724 (precision-wound axialfor aerial operations and drum-spool wound for ground and underwaterapplications, preferably or any variant thereof using the previouslydescribed fiber payout means); an actively cooled heat exchanger 726; apassive heat radiator 728, and a high power fiber coupler 730 thatconnects the spooler 720 in a modular fashion to the vehicle.

In this embodiment, the primary power of the laser 518 is intended forindustrial or military purposes and the output of the fiber spooler 720is connected by output fiber 731 to a laser targeting ball 732. Thetargeting ball 732 contains a real-time active beam focusing structure734 that contains a diverging lens means 736 and a real-time variablerange focusing lens means 738, which causes high energy beam 740 to passthrough optional laser window 742 and to be focused at a point 744beyond the vehicle that is to be determined by other sensors onboard thevehicle. The vehicle carries an auxiliary power unit (APU) 746 thatprovides dedicated power to cooling system 748 that maintains the fiberspooler 720 within its optimal operating temperature range throughout amission. Two or more parallel fibers may run to this vehicle: onecarrying optical power for direct use by the laser targeting ball 732and a second one for use in powering the locomotion of the mobilityplatform.

FIG. 23 shows an unmanned aerial vehicle 750 comprising of primary wingstructures 752; stabilizer fins 754; propulsion air intake 756; andpropulsion unit 758. The vehicle 750 is retrofitted with a lowerstabilizer fin 754 towards the rear of the vehicle 750 that serves as amounting post for high power fiber spooler 762 (although this mechanismmay be mounted anywhere on the vehicle provided the mounting locationprevents interaction or entanglement, and thus breakage, of the fiberwith the propulsion means). The fiber spooler 762, as previouslydescribed, has a high thermal conductivity regeneratively cooled heatexchanger 760 and is equipped with a fiber pay-out guard 764 thatprevents the trailing fiber 766 from being interfered or damaged by thepropulsion unit 758. The fiber 766 from spooler 762 leads forwardthrough the fuselage of the UAV 750 where it connects to laser head 768.Beam focusing optics cause laser radiation 770 to focus on point 771external to the vehicle 750.

The vehicle 750 is assumed to be equipped with a reconnaissance,surveillance, and target acquisition (RSTA) ball 772 or its functionalequivalent, which surveys the field of action using a variety of sensingtechnologies and conveys that information to onboard avionics controland targeting system 774. The targeting system, in turn, causes thelaser targeting ball 768 to lock its orientation in real-time to thetarget point 771 designated by the RSTA ball 772. Feedback between thesetwo systems can be used to actively re-target beam 770 in real-timepending live assessment by RSTA ball 772 and the vehicle onboard poseestimator (which produces real-time estimates of both position andattitude). Knowing all of these pieces of information allows for thebeam to be targeted, and remain on target, to a geographical fixedposition regardless of the vehicle platform's position and attitude.

While the vehicle 750 disclosed in FIG. 23 is largely a battlefielddevice, the same components installed in an autonomous underwatervehicle could be used effectively for removal of obsolete oil productionplatforms (by offering a precise means of cutting off large tubularsteel column elements) without the need for dangerous commercial humandiving operations, which is presently the rule for such work.

Other variants on this same theme include: 1) surface-based andsubterranean mining operations (where a high intensity beam will causerock to heat and fracture, making it possible to easily remove materialof interest. While there have been attempts to use down-hole lasers indrilling operations, no one has attempted to have a mobile robot layingits own power fiber while it goes to work); 2) on mobile ground andaerial vehicles for military applications: a focused targeted beam canbe used for local theater “shoot down” applications (e.g., defendingagainst other drones while not having humans in the area); 3) on mobileground, underwater, and aerial vehicles for salvage operations (e.g.,cutting pieces off for removal); and 4) on mobile ground and aerialvehicles for demolition (e.g., collapsing an old and dangerous bridge orbuilding).

The present invention is described in terms of a preferred illustrativeembodiment and alternative embodiments of specifically-describedapparatuses and systems. Those skilled in the art will recognize thatyet other alternative embodiments of such apparatus and systems can beused in carrying out the present invention. Other aspects, features, andadvantages of the present invention may be obtained from a study of thisdisclosure and the drawings, along with the appended claims.

We claim:
 1. An optical energy transfer and conversion systemcomprising: an optical power source capable of generation of highoptical energy; an actively cooled fiber spooler made up of a highthermal conductivity material; a length of fiber for transmission ofsaid high optical energy, said length of fiber circumscribing at leastpart of said fiber spooler and optically connected to said optical powersource; a remote mobile platform; at least one high power opticalcoupler having a first end and a second end, said first end of said atleast one high power optical coupler connected to said length of fiberand said second end of at least one high power optical coupler connectedto said remote mobile platform; and a power extraction subsystem on saidremote mobile platform, said power extraction subsystem having anoptical energy input for receiving high optical energy, said opticalenergy input connected to said length of fiber, a refractory beam dumphaving a cavity and at least one heat exchanger channel, a refractorytarget within said cavity, beam forming optics orientated to receivesaid high optical energy from said optical energy input and direct thereceived said high optical energy to said refractory target; an array ofthermoelectric converters, said thermoelectric converters having aninterior side and an exterior side, said interior side connected to saidrefractory beam dump and said exterior side exposed to a coldenvironment creating a temperature gradient; and wherein said highoptical energy is converted to another form of energy usable by saidremote mobile platform.
 2. The system of claim 1 wherein said fiberspooler further comprises: a housing having a longitudinal axis, ahousing sidewall, an external sidewall surface, and an internal sidewallsurface; at least one mandrel radially within said housing having amandrel sidewall, said mandrel sidewall and said housing sidewalldefining an annular fiber feed channel therebetween, said at least onemandrel having at least one winding surface defining at least onecircumferential groove, said mandrel sidewall having at least onecircumferential channel formed therein; an active cooling system havinga coolant inlet and a coolant outlet, both in fluid communication withsaid at least one circumferential channel; and a plurality of panelsprotruding radially outwardly from said external sidewall surface ofsaid housing.
 3. The system of claim 2 wherein said optical power sourceis a laser.
 4. The system of claim 3 wherein said length of fiber ispulled out linearly in a direction parallel to the center axis of saidat least one mandrel.
 5. The system of claim 4 wherein said high opticalenergy is in the range of kilowatts to tens of megawatts.
 6. The systemof claim 5, wherein said actively cooled fiber spooler is mounted onsaid remote mobile platform.
 7. The system of claim 6, wherein saidremote mobile platform is a planetary rover.